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Old 10-24-2022, 07:20 AM   #21
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I don’t think I’d discount the method till I did some actual testing. Sure, on the surface it seems pretty dumb, but think about the way a screw would move through the fibers and point the severed ends towards the point of the screw. This would lock the screw in place really firmly. Like a ring shank on steroids.
If the screw was driven in with a driver, the torn ends of the fiber would be oriented parallel to the threads instead of perpendicular. Interesting to think about.
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Old 10-24-2022, 07:32 AM   #22
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Originally Posted by Bmarler View Post
I don’t think I’d discount the method till I did some actual testing. Sure, on the surface it seems pretty dumb, but think about the way a screw would move through the fibers and point the severed ends towards the point of the screw. This would lock the screw in place really firmly. Like a ring shank on steroids.
If the screw was driven in with a driver, the torn ends of the fiber would be oriented parallel to the threads instead of perpendicular. Interesting to think about.
I agree.... I am not discounting it at all...different cultures often prove our way of thinking lopsided.

I have worked enough with wooden boats to know that screws in older, wet wood often strip way too easily from overtightening. The fact that on a wooden boat, the wood absorbs water and planks/frames swell.

The method described might be superior to screwing screws. Can't say for sure it works well, but a well known and used yard may know/think differently.
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Old 10-24-2022, 11:08 AM   #23
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I can tell you this whole question was thought about and tested with various fastener measurements etc. years ago after I witnessed this spectacle. I can assure you that in the instance of this shrimper the scheme was a bad idea. I wrote a paper on this over thirty years ago and gave it to the USCG New London where a number of wood hull experts were called in looking for some magic instrument they could use for fastener inspection. I brought ultrasonics to the game but wasn’t feasible for them. This was right after the El Toro accident. I didn’t think a paper like this belonged here but I could give you some of the hi lights later on when I get home.

Rick
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Old 10-24-2022, 11:38 AM   #24
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I can tell you this whole question was thought about and tested with various fastener measurements etc. years ago after I witnessed this spectacle. I can assure you that in the instance of this shrimper the scheme was a bad idea. I wrote a paper on this over thirty years ago and gave it to the USCG New London where a number of wood hull experts were called in looking for some magic instrument they could use for fastener inspection. I brought ultrasonics to the game but wasn’t feasible for them. This was right after the El Toro accident. I didn’t think a paper like this belonged here but I could give you some of the hi lights later on when I get home.

Rick
i'd like to see this please. i've been involved with engineered wood products all my working life and find the subject interesting. like you say, could be a bit much for this forum, but still...
you are quite right about doing forensic diagnosics on the can be difficult as there's no easy way to examine the fiber structure of the sample. x-ray would be tough with the way the screw would obscure the wood fiber. newer high def x-ray might give a better picture but i don't have access to that technology. taking a slice and examining it under a microscope might give a reasonable picture, but preparing the sample relies heavily on the talent of the person doing the prep. freezing the sample before slicing perhaps? i don't know. very hard to get a good sample without disturbing the structure. interesting subject though.
you were there to see it first hand, so i'd defer to your knowledge of the subject, but really i'd love to see the research.
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Old 10-24-2022, 08:06 PM   #25
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Bmarler you have it about right on all counts regarding NDT testing of hull plank fasteners so I will add this and please understand I’m not trying to blow my own horn here it’s just the way it was.

In 1995 I was contacted by USCG’s Research & Development Center’s Kurt Hansen to discuss demonstrating my ultrasonic equipment and techniques that I’d used for the USN MSO minesweepers and USS Constitution and various Lloyd’s of London surveys. They were looking for a practical NDT method to ascertain hull plank fasteners. The entire program was driven by the recent El Toro passenger vessel casualty on the Chesapeake. I and four or five other surveyors and several NDT equipment firms all met at a wooden test vessel in East Haven, CT. The procedure included demonstration of different equipment and methods at four different locations of a 40’ wood small passenger ferry now out of service.

My equipment consisted of a Krautkramer Branson USD-10 and Sonatest 160 and various common and custom focused probes. Before starting I informed the Coast Guard that since typical hull plank fastener screws come to a sharp point I could not receive a back wall signal and therefore no information. That my equipment was reliable and repetitive with bolts and shafts that terminate with a flat. They however were adamant that I attempt shooting screws only to confirm my advice. Bolts however provided sound readings on wastage, cracks, corrosion of stainless bolts and dezincafication of bronze bolts. In conclusion only real time X-Ray could provide decent visual information on screws but only those where the physical characteristics allowed access for their equipment. The X-Rays did not reliably show small degrees of wastage or reduction of fastener diameter. Plus the equipment and operation is prohibitively expensive and legally cumbersome a moving radioactive isotopes across state lines.

Rick
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Old 10-25-2022, 06:53 AM   #26
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Interesting stuff. My thought with the hammer screws is the way the grain would respond to the screw. As soon as the screw starts wasting, that effect is diminished. Same as nail fastened planks. I remember as a kid growing up in Sitka, we would scour the beach and find double ended nails from old Russian boats. Copper if I remember correctly. After many decades they were still in fantastic condition.
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